1. Field of the Invention
The invention relates to a method of flying changing of working rolls in continuous casting and rolling installations and hot strip rolling mills, in particular in continuous hot strip rolling trains.
2. Description of the Prior Art
Working rolls of a rolling stand are naturally subjected to wear which can lead to quality loss of the surface of a rolled strip.
To prevent this, an exchange of rolls is needed from time to time.
For hot rolling, to-be-rolled strip should be heated to a necessary temperature, this being the case even when it is rolled immediately after casting. When a short furnace is used without a buffer or the furnace is completely omitted because of a continuous casting and rolling, a continuous rolling operation of the casting-rolling operation need be stopped for changing the working rolls. Therefore, the loss of production is not prevented.
A continuous casting and rolling operation with long casting runs is not possible without loss of quality of the strip surface.
During cold rolling operation, this is not a problem, because here the strip is stopped, and then the roll exchange is carried out.
In CSP continuous operation, this is not possible because the casting process is directly connected with the rolling process and cannot be stopped. The stoppage of the casting process would immediately lead to disruption of casting, and the production process would be interrupted.
Therefore, it is important that when a working roll exchange must be carried out during casting, it should also be carried out during rolling, i.e., with a running strip.
However, the roll exchange can be carried out only with an open rolling stand.
If a respective rolling stand is open, the rolling cannot take place in this rolling stand and, thus, no thickness reduction would take place. To compensate for this, the reduction of the open rolling stand should be distributed between surrounding rolling stands, i.e., the engaged rolling stands should take over additionally the rolling work of the open rolling stand during the roll exchange. Failing this, the possibility of the band tension regulation would be normally taken over by a loop lifter that is normally arranged in a continuous rolling train between two following one another, rolling stands. However, this is not any more possible because of the open rolling stand. If despite of this, a loop lifter, which is arranged in front of or behind the open rolling stand, is active, the strip, as the case may be, would be pressed against the upper working roll of the open rolling stand. In this case, the roll exchange would not be possible.
The object of the invention is to enable a flying working roll exchange in a casting and rolling installation or in a continuously operating hot strip rolling mill and, thereby, to provide for shortening/elimination of the buffer time in the furnace, shortening of the furnace, reduction of investment and a smaller energy consumption, and thereby, for cost-effective production process.